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Need Help w/an AR.

2K views 17 replies 11 participants last post by  Markp 
#1 ·
I recently assembled two ARs. Both kits from Model1 and both receivers are DPMS. One works perfect while the other is constantly jamming. The rounds are not ejecting from the chamber, they stick in the chamber and I need to use a cleaning rod to knock them out. There is nothing wrong with the extractor. I cleaned the chamber/bore and lubed the bolt, all the basic stuff. I'm thinking that the upper was not headspaced correctly but not sure as my AR experience is limited to carrying an M4 for 3 yrs. Whenever I had a problem like this I gave it to the Armory. Any suggestions??
 
#3 ·
+1 on what gunbug said. I've run into the same problem numerous times. I was told by an armorer to polish the chamber with a thin scotch pad wrapped around a chamber brush and turned in a cordless drill. I was hesitant to try it but did and it worked beautifully.
 
#4 ·
I would try checking the headspace before I did anything. If the headspace is off Model1 might take it back, but I bet they won't if you've done anything to it. If the headspace is ok then polish the chamber to see if that is the problem. Is the extractor tearing the rim off of the cartridge case? If not A Dfender ring might help some. Is the barrel 16" or shorter, because the pressure might not of dropped low enough before the bolt opened for the case to be extracted (although if you're having to tap them out with a cleaning rod its probably a rough chamber). I take it these are factory loads that you are using.
 
#5 ·
I considered that It might not be getting enough gas, short brl or gas port not wide enough, but I don't think that is it b/c the rounds are a bitch to get out. Which is also the same reason I don't think it is the extractor, it is tearing the rims up pretty badly. I'll check the headspace and then try pollishing the chamber. Thank you guys!! I'm pretty sure the headspace is ok but that was the only thing I could think of. I hadn't heard of polishing the chamber before!
 
#6 ·
Are you using reloaded ammo?

A friend reloaded some surplus stuff and he had the same problem in his AR. It wasn't resizing right, we guessed the cases were thicker then comercial stuff and a hand press wasn't enough to do the job? These reloads did the same thing in a Mini14 too, wouldn't eject and boogered up the rim of the case. He reloaded some Winchester brass and it ran fine.

Just my guess but the other are most likely right.
 
#8 ·
Something to ponder is what type spring and color insert are you using for the extractor in the bolt. Shorter barrels (<16") use a black colt insert and a wolf HD spring (or equivalent). Look into these before you screw with the enlarging the gas port size. Also, what weight buffer are you using ?? Do you have a chrome chamber ??
 
#16 ·
Yep, I was pissed this weekend when my AR stopped working! I am not sure what's wrong. It might be ammo. I was using Wolf, which I hear is crap. It also might be that I didn't run the rifle wet (or wet enough).

It would go bang and not extract the round, it would be jammed half extracted. I think it's the ammo because the week before it would cycle but jammed on feeding frangible ammo (wouldn't pick it up). Prior to that, I cycled 200 rounds with no failures to feed or extract. Ammo was different all three times, this is a DPMS CMP with the HBAR barrel.

Any ideas? I think it's picky about ammo. I couldn't find any problems while cleaning it.

Mark
 
#12 ·
Congrats!

Glad to hear that you got it worked out. I have run into the same issue w/ Model1 Sales. In one case, I had to throat and finish ream the chamber in order to get a round to seat fully. For future reference, the green scotch pad method is the least invasive way to clean up a chamber. I takes very little away in terms of actual metal. If you followed the tecchnique you described, you should be fine! I use an in and out technique to create a swirl pattern inside the chamber, kind of like polishing brake slave cylinders or V8 cylinders.

One thing to always remember: Never mess with the gas port size! A burr in the bore can ruin your whole day! Not to mention the really heavy recoil if you overbore it! Accuracy tends to suffer a lot under these circumstances.


Bellson<img>
 
#13 ·
I wasn't about to enlarge the gas port, the brl isn't that short. I'm glad you guys mentioned polishing the bore, the only thing I could think of was headspace. I knew the problem was in the chamber and not with the ejector or anything else. I just didn't know what was wrong with the chamber. I figured someone here would know! Thank you guys for the help!
 
#14 ·
It was a rough chamber.
I've had the same exact experience with a DPMS upper I bought several years ago. It wouldn't eject the empty casings all the time and the brass was showing signs of a gouged chamber. It would've been impossible to full length resize. Must've had a chip or burr when maching the chamber or possibly not enough coolant? I purchased the upper new/complete from a vendor at a local gunshow. He said he'd take it back to his shop and polish it up. The brass bulges were so deep, I told him I felt it was a manufacturing defect and wanted the barrel replaced. It was sent back to DPMS and was replaced with a new upper n/c.
 
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